THE GASTROINTESTINAL HANDLING AND METABOLISM OF [1-C-13]PALMITIC ACIDIN HEALTHY WOMEN

The gastrointestinal handling and metabolism of [1-C-13]palmitic acid given as the free fatty acid was examined in six healthy women by meas uring the excretion of C-13-label in stool and in breath as (CO2)-C-13 . The gastrointestinal handling of [1-C-13]palmitic acid was compared with the apparent absorption of dietary lipid by measuring lipid losse s in stool. The variation both within and between subjects was determi ned by repeating the study in the same individuals on separate occasio ns. The time course for excretion of label in stool over the five-day study period followed a common pattern, with most of the label excrete d over the first two days of the stool collection. C-13-Label excreted in stool over the five-day study period was 14.3 +/- 9.8% of that adm inistered and on repeating the trial was 31.6 +/- 24.7% (not significa ntly different due to variability); there was poor agreement within su bjects. Lipid excreted in stool expressed as a percentage of ingested lipid was 5.2 +/- 4.4% in Trial 1 and 5.9 +/- 4.0% in Trial 2, and was the same in each individual on repeating the trial. There was no clea r relationship between the excretion of C-13-label and lipid in stool (Trial 1: R = -0.43, P > 0.40; Trial 2: R = -0.02, P > 0.97). On the f irst occasion, 22.0 +/- 4.5% of the administered label was excreted on breath over the 15-h study period and on repeating the trial was 15.8 +/- 9.5% (not significantly different) with poor repeatability in a g iven individual. There was an inverse relationship between the proport ion of C-13-label excreted in stool and that excreted on breath in Tri al 1 (R = -0.80, P > 0.06) with a weaker association observed in Trial 2 (R = -0.49, P > 0.32). Correcting for differences in the apparent a bsorption of label reduced the variability in its excretion in breath observed between subjects, particularly in Trial 2. It is concluded th at although there are differences in the gastrointestinal handling of [1-C-13]palmitic acid both within and between healthy adults, the post prandial oxidation of absorbed substrate was similar. The assumptions underlying these observations need to be examined by characterizing th e nature of C-13-label in stool.